Nutrient utilisation and weathering inputs in the Peruvian upwelling region since the Little Ice Age

For this study two sediment cores from the Peruvian shelf covering the time period between the Little Ice Age (LIA) and present were examined for changes in productivity (biogenic opal concentrations (bSi)), nutrient utilisation (stable isotope compositions of silicon (δ30Siopal) and nitrogen (δ15Nsed)), as well as in ocean circulation and material transport (authigenic and detrital radiogenic neodymium (εNd) and strontium (87Sr/86Sr) isotopes). For the LIA the proxies recorded weak primary productivity and nutrient utilisation reflected by low average bSi concentrations of ~10%, δ15Nsed values of ~ +5‰ and intermediate δ30Siopal values of ~+0.97‰. At the same time the radiogenic isotope composition of the detrital sediment fraction indicates dominant local riverine input of lithogenic material due to higher rainfall in the Andean hinterland. These patterns were caused by permanent El Niño-like conditions characterized by a deeper nutricline, weak upwelling and low nutrient supply. At the end of the LIA, δ30Siopal dropped to low values of +0.6‰ and opal productivity reached its minimum of the past 650 years. During the following transitional period of time the intensity of upwelling, nutrient supply and productivity increased abruptly as marked by the highest bSi contents of up to 38%, by δ15Nsed of up to ~ +7‰, and by the highest degree of silicate utilisation with δ30Siopal reaching values of +1.1‰. At the same time detrital εNd and 87Sr/86Sr signatures documented increased wind strength and supply of dust to the shelf due to drier conditions. Since about 1870, productivity has been high but nutrient utilisation has remained at levels similar to the LIA indicating significantly increased nutrient availability. Comparison between the δ30Siopal and δ15Nsed signatures suggests that during the past 650 years the δ15Nsed signature in the Peruvian Upwelling area has most likely primarily been controlled by surface water utilisation and not, as previously assumed, by subsurface nitrogen loss processes in the water column

Household networks and emergent territory: a GIS study of Chumash households, villages and rock-art in South-Central California

Elite households of the Californian Chumash have been studied in order to understand the development of Late Holocene hunter-gatherer alliance networks. Equally, models of what has been termed ‘tribelet territories’ have been used to describe land ownership within larger Californian concepts. Surprisingly little research has explicitly addressed issues of how such territories may have developed. In this article, we turn to DeLanda’s philosophy of social complexity to consider how Chumash households may have underpinned the development of tribelet territories and the political implications for their articulation with wider alliances. Importantly, utilizing Geographic Information Systems (GIS), we analyse potential mobility patterns in relation to households, villages and rock-art locales in a case from the Emigdiano Chumash. The results suggest that the painting of rock art was imbricated within processes of territorialization, and that the local placement of art reflects which villages were home to particularly high-status households

Polarization investigation of a tunable high-speed short-wavelength bulk-micromachined MEMS-VCSEL

We report the investigation of the state of polarization (SOP) of a tunable vertical-cavity surface-emitting laser (VCSEL) operating near 850 nm with a mode-hop free single-mode tuning range of about 12 nm and an amplitude modulation bandwidth of about 5 GHz. In addition, the effect of a sub-wavelength grating on the device and its influence on the polarization stability and polarization switching has been investigated. The VCSEL with an integrated sub-wavelength grating shows a stable SOP with a polarization mode suppression ratio (PMSR) more than 35 dB during the tuning

A National Survey of Teachers on Antiretroviral Therapy in Malawi: Access, Retention in Therapy and Survival

BACKGROUND: HIV/AIDS is having a devastating effect on the education sector in sub-Saharan Africa. A national survey was conducted in all public sector and private sector facilities in Malawi providing antiretroviral therapy (ART) to determine the uptake of ART by teachers and their outcomes while on treatment. METHODOLOGY/PRINCIPAL FINDINGS: A retrospective cohort study was carried out based on patient follow-up records from ART Registers and treatment master cards in all 138 ART clinics in Malawi; observations were censored on September 30(th) 2006. By this date, Malawi's 102 public sector and 36 private sector ART clinics had registered a total of 72,328 patients for treatment. Of these, 2,643 (3.7%) were teachers. Adjusting for double-registration caused by clinic transfers, it is estimated that 2,380 individual teachers had ever accessed ART. There were 15% of teachers starting ART in WHO clinical stage 1 or 2 with a CD4-lymphocyte count of <or=250/mm(3) and 85% starting in stage 3 or 4. By 30(th) September 2006, 1,850 teachers were alive on ART (3.5% of all teachers in Malawi). The probability of being alive on ART at 6-months, 12-months, 18-months and 24-months after treatment initiation was 84%, 79%, 75% and 73% respectively. Retention in treatment was better for women (adjusted HR = 1.8) and in those starting ART in WHO Clinical Stage 1 and 2 (adjusted HR = 1.8). CONCLUSION/SIGNIFICANCE: Rapid scale up of ART has allowed 2,380 HIV-positive teachers to access life-prolonging treatment. There is evidence that this intervention can help to mitigate some of the shortages of teaching personnel in resource-poor countries affected by a generalised HIV epidemic

A review of the stable istotope bio-geochemistry of the global silicon cycle and its associated trace elements

Silicon (Si) is the second most abundant element in the Earth's crust and is an important nutrient in the ocean. The global Si cycle plays a critical role in regulating primary productivity and carbon cycling on the continents and in the oceans. Development of the analytical tools used to study the sources, sinks, and fluxes of the global Si cycle (e.g., elemental and stable isotope ratio data for Ge, Si, Zn, etc.) have recently led to major advances in our understanding of the mechanisms and processes that constrain the cycling of Si in the modern environment and in the past. Here, we provide background on the geochemical tools that are available for studying the Si cycle and highlight our current understanding of the marine, freshwater and terrestrial systems. We place emphasis on the geochemistry (e.g., Al/Si, Ge/Si, Zn/Si, δ13C, δ15N, δ18O, δ30Si) of dissolved and biogenic Si, present case studies, such as the Silicic Acid Leakage Hypothesis, and discuss challenges associated with the development of these environmental proxies for the global Si cycle. We also discuss how each system within the global Si cycle might change over time (i.e., sources, sinks, and processes) and the potential technical and conceptual limitations that need to be considered for future studies

Public health triangulation: approach and application to synthesizing data to understand national and local HIV epidemics

<p>Abstract</p> <p>Background</p> <p>Public health triangulation is a process for reviewing, synthesising and interpreting secondary data from multiple sources that bear on the same question to make public health decisions. It can be used to understand the dynamics of HIV transmission and to measure the impact of public health programs. While traditional intervention research and metaanalysis would be ideal sources of information for public health decision making, they are infrequently available, and often decisions can be based only on surveillance and survey data.</p> <p>Methods</p> <p>The process involves examination of a wide variety of data sources and both biological, behavioral and program data and seeks input from stakeholders to formulate meaningful public health questions. Finally and most importantly, it uses the results to inform public health decision-making. There are 12 discrete steps in the triangulation process, which included identification and assessment of key questions, identification of data sources, refining questions, gathering data and reports, assessing the quality of those data and reports, formulating hypotheses to explain trends in the data, corroborating or refining working hypotheses, drawing conclusions, communicating results and recommendations and taking public health action.</p> <p>Results</p> <p>Triangulation can be limited by the quality of the original data, the potentials for ecological fallacy and "data dredging" and reproducibility of results.</p> <p>Conclusions</p> <p>Nonetheless, we believe that public health triangulation allows for the interpretation of data sets that cannot be analyzed using meta-analysis and can be a helpful adjunct to surveillance, to formal public health intervention research and to monitoring and evaluation, which in turn lead to improved national strategic planning and resource allocation.</p

Direction-Selective Circuitry in Rat Retina Develops Independently of GABAergic, Cholinergic and Action Potential Activity

The ON-OFF direction selective ganglion cells (DSGCs) in the mammalian retina code image motion by responding much more strongly to movement in one direction. They do so by receiving inhibitory inputs selectively from a particular sector of processes of the overlapping starburst amacrine cells, a type of retinal interneuron. The mechanisms of establishment and regulation of this selective connection are unknown. Here, we report that in the rat retina, the morphology, physiology of the ON-OFF DSGCs and the circuitry for coding motion directions develop normally with pharmacological blockade of GABAergic, cholinergic activity and/or action potentials for over two weeks from birth. With recent results demonstrating light independent formation of the retinal DS circuitry, our results strongly suggest the formation of the circuitry, i.e., the connections between the second and third order neurons in the visual system, can be genetically programmed, although emergence of direction selectivity in the visual cortex appears to require visual experience